1. Field of the Invention
The present invention relates to a water-cooled vertical engine having a crankshaft disposed substantially vertically and being provided with a combustion chamber cooling water jacket for cooling the surroundings of a plurality of combustion chambers, and an outboard motor equipped with the water-cooled vertical engine.
2. Description of the Related Art
As a vertical engine for an outboard motor, a water-cooled engine is generally used. In this type of water-cooled engine, when a cylinder block and a cylinder head are equally cooled with cooling water, if the cylinder head, which generates a comparatively large amount of heat, is cooled to an appropriate temperature, then the cylinder block, which generates a comparatively small amount of heat, tends to be overcooled. An outboard motor cooling structure that can solve such a problem and cools both the cylinder head and the cylinder block to appropriate temperatures is known from Japanese Patent Application Laid-open No. 61-167111.
In embodiments and modification thereof described in this publication (ref. FIG. 2, FIG. 2a to FIG. 2c, FIG. 3, FIG. 3a and FIG. 3b), by supplying low temperature cooling water from a cooling water pump to a cylinder head water jacket and supplying the cooling water having its temperature increased thereby to a cylinder block water jacket, the cylinder block is prevented from being overcooled while the cylinder head is cooled sufficiently.
However, in the above-mentioned conventional arrangement, since the cooling water from the cooling water pump is only supplied from the highest position or the lowest position of the cylinder head water jacket, there is the problem that the temperature of the cooling water within the water jacket might not be uniform in the vertical direction. That is, when the cooling water is supplied from the highest position of the water jacket, the temperature around a combustion chamber at the lowest position is higher than that around a combustion chamber at the highest position, whereas when the cooling water is supplied from the lowest position of the water jacket, the temperature around the combustion chamber at the highest position is higher than that around the combustion chamber at the lowest position, so that it is difficult to provide suitable combustion conditions for all the combustion chambers.